On arrival, Ms May said: “The UK is leaving the EU, but we will continue to play a full role until we leave and we will be a strong and dependable partner after we have left.

“It's in the interests of both the UK and the EU that we continue to work closely together, including at this summit.”

Meanwhile, Mr Tusk said he would be the “happiest one” if the UK reversed the decision to quit and stuck with EU membership for years to come.

He told reporters: “It's not our choice and if you ask me I would prefer 28 members not only for the next month, but also for the next years and decades.

“After the decision in the UK we have to respect the decision of the referendum. If it is reversible or not, this is in the British hands.

“I would be the happiest one if it reversible but we now we have to start our formal works.”

Leaders will discuss trade rules when the European Council continues on Friday, including anti-dumping measures.

Mrs May will then hold talks with European Commission president Jean-Claude Juncker, which No 10 sources said would be an “opportunity to establish a relationship” and talk about “how we see the process ahead”.